Introduction

Aural hematoma (AH) refers to the accumulation of blood in the ear cartilage and the lacuna between the cartilage and skin.¹ Both dogs and cats may suffer from AH, but dogs are more susceptible.² The source of bleeding in AH may be the branches of the auricular arteries and veins within, under, or between the cartilage layers.³ The pathogenesis of AH has been demonstrated to involve atopic dermatitis, otitis externa, ear mites, trauma, and degenerative changes in auricular cartilage.^1,4,5 At the initial stage of AH, fibrin formation without treatment can lead to fibrosis, contraction, and thickening of the auricle, resulting in a cauliflower-like appearance.⁶ Conservative treatment is common, with AH fluid aspiration and AH fluid aspiration combined with dexamethasone infusion.³ However, these treatments may lead to AH recurrence and the formation of abscesses.^1,7 Platelet-rich plasma treatment may be an alternative to nonsurgical treatment.⁸ Surgical treatments include Penrose drainage tubes, incisional drainage with sutures, continuous vacuum drainage, and carbon dioxide laser incision drainage.^5,9–11 Common postoperative complications include AH recurrence and auricular thickening; additional complications include blocked drainage tubes, auricle necrosis, permanent scarring, and cauliflower-like atrophy.^1,9,11

Shape memory polymers (SMPs), as a type of smart material, can retain their shape under external stimulation by transforming polymer chain conformations.¹² Among biofriendly SMPs, polycaprolactone (PCL) has been widely studied because of its strong mechanical properties, tunable transition temperature, designable structure, and tunable responsivity.¹² This material can be blended with other polymers and has a low melting temperature.¹³ The tunable transition temperature enables PCL to soften at high and harden at low temperatures,¹² making it an ideal material for manufacturing customized AH splints.

Other splinting techniques, such as stents and x-ray films, have been employed to relieve the suture tension of incisional drainage with sutures.^14,15 However, these techniques may not effectively ensure uniform suture tension across the entire auricle. Application of stents may be associated with auricle infection and tissue necrosis.¹⁶ The plasticity of PCL material allows custom shaping of the splints to exert uniform and consistent pressure on the AH area when applied to the auricle’s concave and convex surfaces.¹³ This study aimed to report cases of AH in 7 dogs and 3 cats treated with PCL splint application. To our knowledge, a clinical protocol of PCL splint application for treating AH in dogs and cats has yet to be described.

Methods

Polycaprolactone splint preparation

For surgical planning, AH was classified as generalized (AH involved the entire pinna surface) or localized (AH involved a part of the pinna surface). The long-axis and short-axis distances of the affected area were measured. On the basis of these measurements, the material area required for surgery was estimated and the PCL splint material of appropriate size was selected (PCL splint; Tian Hong Medical Technology Co). The selected PCL splint material was pressed against the auricle’s concave and convex surfaces, ensuring that the material wholly conformed to the shape of the auricle. Regarding generalized AH, the PCL material was trimmed along the edge of the auricle to ensure that it did not exceed the size of the auricle. Ultimately, PCL splints that met both surfaces of the auricle were obtained (Figure 1). Regarding localized AH, the PCL material was trimmed along the area with a 0.5-cm margin extending beyond the edge of the hematoma.

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The steps in creating the polycaprolactone (PCL) splints applied in treating aural hematoma (AH) in 7 dogs and 3 cats between December 2022 and June 2024. A—Attach the PCL splint material against the auricle. B—Trim the material to fit the concave surface of the auricle. C—Trim the material to fit the convex surface of the auricle. D—Obtain the required PCL splints.

Citation: Journal of the American Veterinary Medical Association 2025; 10.2460/javma.24.09.0571

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Polycaprolactone splint application procedure

Each animal was premedicated with dexmedetomidine (0.003 mg/kg, IV) and butorphanol (0.5 mg/kg, IV), followed by induction with propofol (2 to 4 mg/kg, IV, to effect). Anesthesia was maintained with isoflurane in oxygen. The animals were positioned in sternal recumbency. First, the fur of the auricle’s concave and convex surfaces affected by AH was clipped. The auricle was disinfected with iodophor (2% povidone-iodine) and alcohol and covered with a fenestrated sheet. An 18- or 23-gauge needle connected to a 5- to 10-mL syringe was used to drain the hematoma fluid.

In cases of chronic AH, upon aspirating the hematoma fluid, saline was injected into the AH cavity with a 10-mL syringe and the fluid was then reaspirated. This process was repeated 2 to 3 times until fibrin clots and fibrinous material were removed. The precut PCL splints were immersed in 70 to 90 °C water for material softening. After about 10 to 20 seconds, the color of the splints changed to a transparent color, indicating that the material had softened and was ready for shaping.

The splints were removed from the water and placed on sterile gauze to allow moisture to evaporate, and the temperature was decreased to an acceptable range for skin application. The softened splint material was placed against the concave surface of the auricle, pressed to fit completely against the contour of the auricle, and held in position while cooling. Another softened splint material was placed against the convex surface of the auricle, and the splint was shaped as described earlier. To secure the PCL splints to the auricle, 3-0 polyglycolic acid suture on a curved reverse cutting needle was used with a full-thickness interrupted suture pattern (Figure 2).

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The surgical procedure of applying PCL splints to animals being treated for AH. A—Drain all hematoma fluid in the auricle with an 18- or 23-gauge needle connected to a 5- to 10-mL syringe. B—Immerse the prepared PCL splints in a container of 70 to 90 °C water for material softening. C—Shape the PCL splints to fit the auricle’s concave and convex surfaces. D—Secure the PCL splints to the auricle tip with full-thickness interrupted sutures. E—Secure the PCL splints to the auricle margin with full-thickness interrupted sutures. F—The PCL splints are secured firmly to the auricle.

Citation: Journal of the American Veterinary Medical Association 2025; 10.2460/javma.24.09.0571

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For generalized AH, splints were secured at the edge of the auricle with sutures spaced at 1 to 1.5 cm. If the short-axis distance of the affected area exceeded 3 to 4 cm, sutures were also placed in the middle of the auricle at a suture spacing of 1 to 1.5 cm. Regarding localized AH, splints were sutured to the auricle along the edge of the AH area with a suture spacing of 0.5 to 1 cm. It is essential to avoid overtight sutures during the suturing process. Both surfaces of the auricle were disinfected with iodophor (2% povidone-iodine) and alcohol again after the surgery.

Postoperatively, the animals wore Elizabethan collars until suture removal and received ampicillin sodium (20 mg/kg, PO, q 8 h) and meloxicam (0.2 mg/kg, SC, q 24 h) for 3 days. During postoperative care, iodophor (2% povidone-iodine) was used to disinfect the auricle daily until the splints were removed, and the auricle was checked every day for any signs of wrinkling, deformation, or abnormal discharge.

Results

In the present study, 7 dogs and 3 cats underwent PCL splint application (Supplementary Table S1). The representative dog breeds were Golden Retriever (n = 3) and Corgi, Malinois, German Shepherd Dog, and mixed breed (1 each). The mean body weight of dogs was 30.0 ± 7.6 kg, and the mean age of dogs at the onset of AH was 7.4 ± 3.0 years. The representative cat breeds were American shorthair (n = 2) and Ragdoll (1). In these cats, the body weights were 0.8, 6.3, and 3.4 kg, respectively, and the ages at the onset of AH were 0.25, 7, and 0.58 years, respectively. Seven dogs and 1 cat were male, while 2 cats were female.

Three dogs and 1 cat had localized AH, and 4 dogs and 2 cats had generalized AH. Additionally, 6 dogs and 2 cats had initial AH, and 1 dog and 1 cat had recurrent AH. The dog and cat with recurrent AH had been treated by needle aspiration, and the clinical signs recurred within 24 hours. Five dogs and 1 cat had acute AH, and 2 dogs and 2 cats had chronic AH. The mean duration of clinical signs was 2.2 ± 1.2 days for animals with acute AH and 10.0 ± 1.6 days for animals with chronic AH. Tympanitis was diagnosed in 2 dogs. Fungal otitis was diagnosed in 2 cats. In 1 dog and 1 cat, the ears were lacerated as a result of trauma. Labyrinthitis was diagnosed in 1 dog. Otitis externa was diagnosed in 1 dog. In 1 dog, AH occurred secondary to a parasitic infection.

The mean time of PCL splint application was 16.3 ± 4.6 days for all animals. Clinical signs resolved in 5 dogs and 3 cats (8 of 10 AHs [80%]) following removal of the PCL splints. Two dogs (2 of 10 AHs [20%]) experienced AH recurrence, and the time of PCL splint application in these dogs was 10 days. The period between PCL splint removal and recurrence was 7 and 10 days. New PCL splints were reapplied to these dogs and removed at 21 and 23 days. One dog (1 of 10 AHs [10%]) that presented with localized AH exhibited localized wrinkling of the auricle after removing the PCL splints. Six dogs and 3 cats (9 of 10 AHs [90%]) showed no postoperative auricular changes. Following the surgical procedure, 1 dog was treated for tympanitis, 1 dog for a parasitic ear infection, 1 cat for trauma, and 1 cat for fungal otitis. The other animals were treated for their underlying diseases only during splint application.

The follow-up periods ranged from 6 to 8 months (median, 6.5 months; IQR, 13.0 to 20.3 months). There were no recurrent AHs among any patients at the long-term follow-up period. All owners were satisfied with the cosmetic results, except the owner of the dog with localized wrinkling of the auricle. Figure 3 presents the auricle comparison of 3 patients before and after the PCL splint application.

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Comparative pictures of the auricle before and after PCL splint application in 3 patients with AH. All PCL splints are sutured to the auricle and exert uniform and consistent pressure on the AH site. A—The auricle of a dog with generalized AH. B—Postoperative image of the auricle in panel A. C—The auricle of a dog with localized AH. D—Postoperative image of the auricle in panel C. E—The auricle of a cat with generalized AH. F—Postoperative image of the auricle in panel E.

Citation: Journal of the American Veterinary Medical Association 2025; 10.2460/javma.24.09.0571

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Discussion

The present study used PCL splint application to treat AH in dogs and cats, and the mean time of PCL splint application was 16.3 ± 4.6 days for all animals. The mean treatment duration of PCL splint application was similar to Penrose drainage tubes (15 days) and shorter than multiple–drainage-hole surgery (18 days).^5,9 Two dogs experienced AH recurrence, and the time of PCL splint application was 10 days. Because these dogs were treated at the initial stage of the PCL splint application series, we underestimated the duration of splint application necessary for effective treatment. New splints were applied to these dogs for 21 and 23 days, and upon their removal no recurrence of AH was observed. The mean splint application duration of the remaining 8 animals was 17.9 ± 3.5 days, which may have indicated a better suggested time for addressing AH with PCL splints. The recurrence rate of PCL splint application was similar to that of carbon dioxide laser incision drainage (20%), multiple–drainage-hole surgery (16.7%), and Penrose drainage tubes (15%).^9,10,17 No animals experienced recurrence during the long-term follow-up period, which lasted > 6 months. One dog exhibited partial auricular wrinkling, possibly related to overtight suturing during splint application. The remaining animals showed no cosmetic changes in the auricle after the splint application, and the owners were delighted with the cosmetic effect. The cosmetic effect of PCL splint application was similar to that of multiple–drainage-hole surgery, incisional drainage with sutures, and continuous vacuum drainage and significantly better than Penrose drainage tubes.^5,9,11,17

In a previous study,⁹ Penrose drainage tubes had an average cosmetic effect, with only 52.8% of owners rating the cosmetic effect as good; they are challenging to install in cats with small auricle structures and require daily postoperative cleaning to prevent blockage. Regarding incisional drainage with sutures and multiple–drainage-hole surgery, creating incisions or holes in the ear is invasive and causes trauma to the auricle.^11,17 For continuous vacuum drainage, local infection around the drain may occur even with antibiotics postoperatively, ultimately necessitating early drain removal and potentially leading to complications.⁵ Additional treatments, including continuous vacuum drainage, carbon dioxide laser incision drainage, and platelet-rich plasma treatment, are generally accompanied by high costs, suboptimal cosmetic effects, complicated postoperative care demands, and difficulty in treatment implementation alone or simultaneously.^8,10,18

The PCL splint application is a promising alternative treatment for AH in dogs and cats. In the present study, splints were secured to the auricle with full-thickness interrupted sutures. The straightforward procedure of PCL splint application may enable surgeons with varying experience levels to perform operations independently while maintaining efficacy. Auditory canal diseases frequently coexist with AH, including allergic dermatitis and external otitis, which may not be appropriate for invasive surgical procedures.¹⁹ In the PCL splint application, only minor punctures resulting from sutures are left on the auricle instead of incisions or drainage holes. The minimally invasive characteristics of PCL splint application and the biocompatibility of PCL may reduce the risk of tissue reactions.¹³ During postoperative care, we suggest the use of iodophor for daily disinfection to decrease the risk of infection, reducing care demands and the incidence of other complications.

In the present study, the primary component of the splints was PCL, a biofriendly SMP with excellent performance.¹² The superior plasticity of PCL material allows custom shaping of the splints, and the solid mechanical properties maintain the shape of the auricle to a maximum extent during splint application; we believe this significantly improves postoperative cosmetic effects.^12,13 In the PCL splint application, splints are sutured to cover the auricle’s convex and concave surfaces, exerting uniform and consistent pressure on the AH area and reducing the risk of pressure necrosis.

This study’s limitations included the relatively low number of animals and subjective determination of the duration of the PCL splint application. More acute and chronic AH cases are required to clarify the treatment duration for PCL splint application in different conditions.

In this study, PCL splint application had unsatisfactory surgical results in 2 dogs due to premature removal of the PCL splint. The recurrence rate of PCL splint application was similar to that of carbon dioxide laser incision drainage, multiple–drainage-hole surgery, and Penrose drainage tubes. More cases involving AH in dogs and cats are necessary to validate the therapeutic efficacy of PCL splint application. In conclusion, PCL splint application is a promising treatment for AH in dogs and cats. This treatment has the advantages of a simple operational procedure, minimal postoperative care requirements, and sound cosmetic effects.

Supplementary Materials

Supplementary materials are posted online at the journal website: avmajournals.avma.org.

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.